Image display apparatus

ABSTRACT

In the image display device according to the present invention, control is performed such that a condition of not using a subsidiary pixel which corresponds to a specific color among the subsidiary pixels constituting a first pixel is selected as a condition for signal processing to output a signal for designating intensity of each subsidiary pixels constituting the first pixel, and a condition of using a subsidiary pixel which corresponds to a specific color among the subsidiary pixel constituting a second pixel is selected as a condition for signal processing to output a signal for designating intensity of each subsidiary pixels constituting the second pixel adjacent to the first pixel in the first direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image display apparatus.

2. Related Background Art

Japanese Patent Application Laid-open No. H06-261332 discloses a methodfor converting three-primary-color signals into multiple-primary-colorsignals. According to the method, positions of the transmittedthree-primary-color signals on a chromaticity diagram are determined,and three colors are selected from among multiple primary colors basedon the positions thus determined to thereby output the selected threecolors as the multiple-primary-color signals.

Japanese Patent Application Laid-open No. 2003-208152 discloses a colorsignal processing device capable of achieving the display white based onfour or more primary colors for display.

It is widely known that there is more than one solution to colorseparation which is performed for converting three-primary-color signalsinto multiple-primary-color signals. However, according to the methodsdisclosed in Japanese Patent Application Laid-open No. H06-261332 and inJapanese Patent Application Laid-open No. 2003-208152, only one solutionpreselected from among a plurality of solutions is used, irrespective ofa position of the pixel or a display frame, to generatemultiple-primary-color signals.

A display device commonly distributed has a structure in which variouscolors can be displayed based on three primary colors. Use of four ormore primary colors makes it possible, for example, to extend a range ofcolors that can be reproduced. Even in a case where the four or moreprimary colors are used, there is no need to use all the primary colorsto express each color within the range of colors, which can be displayedby less than four primary colors.

The inventors of the present invention have found that there occursvisual interference inherent to a display device that uses four or moreprimary colors.

SUMMARY OF THE INVENTION

An object of the present invention is to suppress reduction in imagequality or to improve image quality in a display device using four ormore colors.

The above object can be attained by an image display apparatus describedbelow. That is, the image display apparatus includes:

a plurality of pixels;

a signal processing circuit; and

a control circuit, in which:

each of the plurality of pixels comprises subsidiary pixelscorresponding to tour or more primary colors;

the plurality of pixels are arranged such that subsidiary pixelscorresponding to a same color are arranged in a first direction;

the signal processing circuit performs signal processing to output asignal for designating intensity of each subsidiary pixels constitutinga pixel, based on an input signal for designating a color to bedisplayed in the pixel;

the control circuit selects a condition for the signal processing tooutput a signal for designating intensity of each of subsidiary pixelsconstituting a first pixel, such that the subsidiary pixels constitutingthe first pixel except for a subsidiary pixel which corresponds to aspecific color is used; and

the control circuit further selects a condition for the signalprocessing to output a signal for designating intensity of eachsubsidiary pixels constituting a second pixel adjacent to the firstpixel in the first direction, such that, among the subsidiary pixelsconstituting the second pixel, a subsidiary pixel which corresponds to aspecific color is used.

As regards the input signal for designating colors displayed in eachpixel, a tristimulus value may be preferably used. An RGB signal or acolor-difference signal may also be used as the input signal. It ispreferable that the RGB signal or the color-difference signal, when usedas the input signal, be converted into a tristimulus value before beingsubjected to signal processing for separating the signal into signalscorresponding to the four or more primary colors.

It is not necessary to meet the condition that, for all adjacent pixels,“the control circuit selects a condition for the signal processing tooutput a signal for designating intensity of each of subsidiary pixelsconstituting a first pixel, such that the subsidiary pixels constitutingthe first pixel except for a subsidiary pixel which corresponds to aspecific color is used”.

It would be enough if the control circuit conducts the control suchthat, at least, a part of the adjacent pixels constituting the imageframe meet the above condition. Moreover, it would be unnecessary thatthe first and second pixels are always fixed. When an image frame isformed, a part of the pixels meet the condition as the first and secondpixels. And, at the time of forming the next image frame, pixels otherthan the first and second pixels of the previous image frame may meetthe above condition of the first and second pixels within the scope ofthe present invention.

And, as a result of the random selection by the control circuit, atleast, a part of the adjacent pixels may meet the above condition withinthe scope of the present invention.

Not all of the adjacent pixels meet the condition as the first andsecond pixels, and the first and second pixels are not fixed, in theeach of following described inventions.

Also, it is possible to adopt another structure described below. Thatis, an image display apparatus includes:

a plurality of pixels;

a signal processing circuit; and

a control circuit, in which:

each of the plurality of pixels has subsidiary pixels corresponding tofour or more primary colors;

the signal processing circuit performs signal processing to output asignal for designating intensity of each subsidiary pixels constitutinga pixel, based on an input signal for designating a color to bedisplayed in the pixel;

the control circuit selects a condition, for a first image, for thesignal processing to output a signal for designating intensity of eachof subsidiary pixels constituting a first pixel, such that thesubsidiary pixels constituting the first pixel except for a subsidiarypixel which corresponds to a specific color is used; and

the control circuit further selects a condition, for a second imageadjacent in time to the first image, for the signal processing to outputa signal for designating intensity of each subsidiary pixelsconstituting the first pixel, such that, among the subsidiary pixelsconstituting the first pixel, a subsidiary pixel which corresponds to aspecific color is used.

Further, according to the present invention, a structure described belowcan be suitably adopted in which the signal processing circuit includes:a first circuit for performing signal processing under the conditionthat the subsidiary pixel except for one which corresponds to a specificcolor is used; and a second circuit for performing signal processingunder the condition that the subsidiary pixel which corresponds to aspecific color is used; and the control circuit selectively designatesone of the first circuit and the second circuit included in the signalprocessing circuit.

In order to selectively designate the first circuit and the secondcircuit, it is possible to select one of the signals outputted from thefirst circuit and the second circuit or to specify that only one of thefirst circuit and the second circuit outputs the signal. When the fouror more primary colors are composed of colors ranging from a firstprimary color to an n-th primary color, a structure described below issuitably adopted.

It is possible to suitably adopt a structure which includes each ofcircuits: a first circuit for performing signal processing under acondition that the first primary color is not used (a first circuit forperforming signal processing on condition that at least three primarycolors except the first primary color are used); a second circuit forperforming signal processing on condition that the second primary coloris not used (a second circuit for performing signal processing oncondition that at least three primary colors except the second primarycolor are used); . . . ; and,an n-th circuit for performing signalprocessing on condition that the n-th primary color is not used (an n-thcircuit for performing signal processing on condition that at leastthree primary colors except the n-th primary color are used).

In the present invention, various colors can be, adopted as the primarycolors. Specifically, selected as the primary colors are a plurality ofcolors that can be visually synthesized in order to make variousrecognizable colors. Examples of such the colors include red, blue,green, and cyan.

It is also possible to adopt the following structures: a structure inwhich a condition for the signal processing is selected based onposition information of pixel; a structure in which a condition for thesignal processing is selected using random numbers; and a structure inwhich a condition for the signal processing is selected based oninformation on a frame.

The present invention makes it possible to suppress reduction in imagequality or to improve image quality.

The problems described above are more noticeable in an image havingpixels of the same color arranged in series or in an image having pixelswith little color difference, particularly in a case where those imagesare static images. According to the present invention, it is possible tosuppress reduction in image quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an image display apparatus according to thepresent invention;

FIG. 2 is a chromaticity diagram for explaining a chromaticity offour-primary-color output;

FIG. 3 is a chromaticity diagram for explaining color separation;

FIG. 4 is a flowchart for explaining an operation of selecting unit forselecting color separation;

FIG. 5 is an explanatory diagram showing in detail color separationprocessing according to a first embodiment;

FIG. 6 is a schematic diagram for explaining a pixel arrangementaccording to the first embodiment;

FIG. 7 is a schematic diagram showing a display state according to thefirst embodiment; and

FIG. 8 is a schematic diagram showing a display state according to aconventional example.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As described above, a display for displaying multiple primary colors(N-primary colors) by juxtaposition additive color mixing includes thesubsidiary pixels whose number (N) is equal to that of the multipleprimary colors, which increases an area of one pixel. Accordingly, auser can easily recognize the subsidiary pixel structure, which causesvisual interference such as vertical stripes due to the pixel structure.A more specific explanation on this point is given below.

The following case is taken as an example. That is, one pixel iscomposed of four subsidiary pixels respectively including RGBC primarycolors, which are horizontally arranged to be adjacent to one another.Such the pixels are aligned in columns to be arranged into a verticalstripe array (a first direction corresponds to a vertical direction of ascreen) in a display. On the display, a certain display region is filledwith a color T (that is, the same color is displayed in a verticaldirection).

In this case, when the color T is separated into three colors of R, G,and B as color separation 1, subsidiary pixels corresponding to a colorC are not illuminated in the display region. As shown in FIG. 8, theunilluminated subsidiary pixels constitute stripes, which can be easilyrecognized as vertical stripes in the display region (shaded subsidiarypixels correspond to the unilluminated pixels). This problem is notlimited to the case where the subsidiary pixels corresponding to thesame color are arranged in a vertical direction. The same problem mayalso be caused in a case where the pixels are arranged to be verticallyadjacent to one another, in which the subsidiary pixels corresponding tothe same color are deviated from one another by 1/p pitch (1 pitchcorresponds to a width of one pixel in a horizontal direction). Here, pis an integer larger than 2. In this case, the unilluminated subsidiarypixels are aligned in a slanting direction (with respect to the firstdirection), which can be easily recognized as oblique stripes.

The same visual interference may occur in a case where subsidiary pixelsare arranged in a vertical direction in one pixel.

According to this embodiment, in a case where the color T can also beseparated into three colors of R, G, and C as color separation 2, thecolor separation 2 and the color separation 1 are used in combination todisplay the display region.

Accordingly, the subsidiary pixels having different illuminationpatterns are arranged in the display region of the same display color,which smoothes out the displayed color intermittently continued in colorreproduction, to thereby alleviate the visual interference. As a result,it is possible to attain high image quality, while promoting stabilityin color reproduction.

It is important for a display to have smooth gradations in color.According to an embodiment of the present invention, continuity indisplayed color can be maintained in a multiple primary color display,which allows a display apparatus to have more tolerance for variationsin display characteristics thereof to thereby attains cost reduction inproduction.

The embodiment according to the present invention is explained below.

An image display apparatus according to the present invention includes aliquid crystal display apparatus, a plasma display apparatus, and anelectron beam display apparatus, each having a plurality of pixels whichare driven in matrix addressed driving method, and preferably includesan image display apparatus in which colors are displayed based onjuxtaposition additive color mixing.

In FIG. 1, input M stimulus value signals 10 (M≧3, M is an integer) eachare for expressing color information of a certain pixel.

Color separation means 20 is a signal processing circuit composed of aplurality of color separators 200 which correspond to circuits from afirst circuit to an n-th circuit respectively. The color separationmeans 20 subjects the input M stimulus value signals 10 to colorseparation at each of the color separators 200 to output the signals asN-primary-color signals.

Here, N is larger than M (N>M), which means that the color separators200 obtain indefinite solutions to color separations. It is preferablethat the color separators 200 perform color separation under appropriatelimiting conditions that are different from one another so that eachobtains different solutions. Such the appropriate limiting conditionsthat are different from one another include: a condition of not using asignal of a specific primary color; and a condition of emphasizing aspecific primary color value.

Under the limiting conditions, when there is no solution correspondingto the N-primary-color signal value, at least one of the N-primary-colorsignals outputted from the color separation means 20 has an unrealizablevalue (negative value, or a value exceeding a maximum tolerable value).

Display information 30 for the input M stimulus value signals issupplied to a selecting unit for selecting color separation 40. Thedisplay information 30 includes display pixel position informationcontaining information on horizontal/vertical position on a screen anddisplay frame information (display frame number). The display pixelposition information or the display frame information does not need tobe exact position information, and a part of the information such as thelower order digit thereof can be used.

The selecting unit for selecting a solution of color separation 40selects one of the solutions to the color separations different from oneanother outputted from the color separation means 20, and outputs theselected solution. The selecting unit for selecting color separation 40may select a solution based on any one of: random number informationgenerated within the selecting unit for selecting color separation 40;display pixel position information; and display frame information.

Here, a solution to the color separation can be obtained by solving thefollowing equation.

=O ⁻¹ ·I·where

is a vector having the input M value signals(i₁,i₂,Λ,i_(M))^(T)as elements;.Iis a matrix with 3 rows and M columns $\begin{pmatrix}I_{1X} & I_{2X} & \Lambda & I_{MX} \\I_{1Y} & I_{2Y} & \Lambda & I_{MY} \\I_{1Z} & I_{2Z} & \Lambda & I_{MZ}\end{pmatrix}\quad$for converting

into a display color system value of, for example, CIE1931XYZ;

is a vector having the output N value signals(o₁,o₂,Λ,o_(N))^(T)as elements;O⁻¹is an inverse matrix of a matrix O with 3 rows and N columns$\begin{pmatrix}O_{1X} & O_{2X} & \Lambda & O_{NX} \\O_{1Y} & O_{2Y} & \Lambda & O_{NY} \\O_{1Z} & O_{2Z} & \Lambda & O_{NZ}\end{pmatrix}\quad$for converting

into a display color system value of, for example, CIE1931XYZ.

A predetermined limiting condition is applied to the inverse matrix, andthe inverse matrix is solved by a known method to obtain the solution.

When there is no solution to the selected color separation, it ispreferable to select another color separation one after another so thata possible solution can be obtained. When no solution is found for anyof the color separations, an error value such as a negative value isoutputted.

An N-primary color image display unit 50 has a structure in which eachcolor pixel is composed of subsidiary pixels of N-primary colors, towhich N-primary-color signals outputted by the selecting unit forselecting color separation 40 are inputted to illuminate each pixel.

Specific examples are provided as follows to describe the presentinvention in detail.

EXAMPLE 1

Example 1 is a specific case where tristimulus value signals areinputted four color separators are provided, and four primary colors areused for display.

In other words, M and N of FIG. 1 are defined as M=3 and k=N=4,respectively.

The tristimulus value adopts AbodeRGB value (primary color points: R(x=0.64, y=0.33); G (x=0.21, y=0.74); and B (x=0.15, y=0.06) and a basicstimulus (D65 light source)), which constitute a color space having widecolor range proposed by Abode Systems, Inc.

Adopted as a chromaticity value for each of the four primary colors is,as shown in FIG. 2, a three-primary-color RGB value of the EuropeanBroadcasting Union (EBU) system (primary color points: R (x=0.64,y=0.33); G (x=0.29, y=0.60); and B (x=0.15, y=0.06), a basic stimulus(D65 light source), and a fourth primary color value (primary colorpoint:.C (x=0.14, y=0.33))).

In a four-primary color display apparatus-thus structured, four colorseparators 200 perform color separations of FIG. 1 each using threeprimary colors out of the four primary colors for the sake of simplecalculation.

For example, a color separator 1 uses primary colors of RGB for colorseparation, a color separator 2 uses primary colors of GCR for colorseparation, a color separator 3 uses primary colors of CBG for colorseparation, and a color separator 4 uses primary colors of BRC for colorseparation. The color separator 1 outputs a set of signals eachdesignating intensity of respective subsidiary pixels of R, G, and B.When the set of signals outputted from the color separator 1 is selectedfor displaying a given pixel, a subsidiary pixel of C is not illuminated(OFF). The color separator 2 outputs a set of signals each designatingintensity of respective subsidiary pixels of G, C, and R. When the setof signals outputted from the color separator 2 is selected fordisplaying a given pixel, a subsidiary pixel of B is not illuminated(OFF). The color separator 3 outputs a set of signals each designatingintensity of respective subsidiary pixels of C, B, and G. When the setof signals: outputted from the color separator 3 is selected fordisplaying a given pixel, a subsidiary pixel of R is not illuminated(OFF). The color separator 4 outputs a set of signals each designatingintensity of respective subsidiary pixels of B, R, and C. When the setof signals outputted from the color separator 4 is selected fordisplaying a given pixel, a subsidiary pixel of G is not illuminated(OFF).

In Example 1, the display information 30 includes the least significantone bit of horizontal/vertical information (IX, IY) based on an inputtristimulus signals 10 to be supplied as display pixel positioninformation, which is necessary and sufficient information for selectinga signal from among signals outputted by the color separation means 20based on four solutions.

The selecting unit for selecting color separation 40 follows anoperation sequence shown by the flow chart of FIG. 4.

The selecting unit for selecting a solution of color separation 40starts operation to set Nmax in Step 1, i.e., the number of the colorseparation means that can be selected.

Then, in Step 2, the selecting unit for selecting color separation 40inputs display pixel position information I1 and I2. In Example 1,. I1and I2 each correspond to one bit of information.

Next, in Step 3, the selecting unit for selecting color separation 40generates a random number, which corresponds to a color separationselection number K based on I1, I2, and Nmax. The random number to begenerated should be in a range of 0 to Nmax, and in Example 1, any oneof 0, 1, 2, and 3 is outputted as K.

After that, in Step 4, the number of searches conducted for colorseparation (hereinafter referred to as the number of searches) N isinitialized to 1.

Then, in Step 5, color separation elements R(K)r G(K), B(K), and C(K)indicated by the color separation selection number K are checked forvalidity. Specifically, for checking the validity, it is judged whetheror not the minimum value for each of the color separation elements isequal to or larger than 0, or whether or not the values for the colorseparation elements include a value exceeding the maximum tolerablevalue, because an invalid solution contains at least one colorseparation element has a negative value or the value exceeding themaximum tolerable value.

When it is judged as valid in Step 5, color separation elementsindicated by the color separation selection number K are outputted inStep 11, and the selecting unit for selecting color separation 40 endsits processing.

When it is judged as invalid in Step 5, the selecting unit for selectingcolor separation 40, starts another selection operation for obtaininganother solution.

In Step 6, the number of searches N is incremented, and in Step 7, it isjudged whether the incremented number N exceeds Nmax, the number of thecolor separation means that can be selected.

When it is judged as N exceeding Nmax, the process moves to Step 10 tooutput an error state.

When it is judged as N being below Nmax, the next color separationselection number K is calculated in Step 9, and the process jumps toStep 5.

The operation of the selecting unit for selecting color separation 40 isdescribed above.

Next, operation for color separation is further explained with referenceto FIG. 5.

As shown in FIG. 5, a case where input tristimulus signals S1, S2, S3,and S4 are inputted is considered. Each of the signals has display pixelposition information and a chromaticity value.

Those signals correspond to pixels having similar chromaticity values,which are arranged to be adjacent to one another as shown in FIG. 6.

The least significant one bit of the display pixel position informationis used as the display pixel position information for horizontalposition and vertical position, and converted by the selecting unit forselecting color separation 40 into the color separation selection numberK in Step 3 of the operation of the selecting unit for selecting colorseparation 40 as described above.

The color separation means 20 supplies the input tristimulus signals tothe four color separators 200 to obtain solutions for color separation.In FIG. 5, “o” and “x” in columns under “color separation” indicatecases where a solution is obtained and where a solution is not obtained,respectively.

The selecting unit for selecting color separation 40 selects the outputfrom the color separators 200, which is indicated as “select colorseparations” in FIG. 5.

A four-primary color image display unit 50 display an image based oncolor separation thus selected. FIG. 7 schematically shows a displaystate, in which unilluminated subsidiary pixels (shaded pixels) arerandomly dispersed in terms of position.

Example 1 discloses the case where color separation is performed usingthree primary colors out of the four primary colors in a four-primarycolor display apparatus, for the sake of simple calculation, and it isalso possible that the color separators 200 perform color separationdifferent from one another by using all the four primary colors.

It is also possible that only one color separator is used, and bychanging parameters for matrix calculation performed by the colorseparator according to locations of pixels, conditions for colorseparation is selected according to each of the pixels.

Example 2

In Example 1, visual interference is eliminated by spatially dispersingthe unilluminated subsidiary pixels. In Example 2, unilluminatedsubsidiary pixels are dispersed in terms of time to eliminate visualinterference.

Similarly to Example 1, the input tristimulus signals of S1 to S4,corresponding to four pixels adjacent to one another, for displayingsubstantially the same color are inputted to the color separation means200. The output of color separators 2 and 3 which have obtainedsolutions to the color separation to the selecting unit for selectingcolor separation 40. At this time, frame information is inputted as thedisplay information 30, which is one bit of information having “0” foran even-numbered frame and “1” for an odd-numbered frame. The selectingunit for selecting color separation 40 selects output from the colorseparator 2 for the even-numbered frame, and selects output from thecolor separator 3 for the odd-numbered frame, and output the selectedoutput. As a result, a three-primary color image display unit 50displays an image in which each frame has unilluminated pixels atdifferent positions.

This application claims priorities from Japanese Patent Applications No.2005-077162 filed on Mar. 17, 2005, and No. 2006-066055 filed on Mar.10, 2006, which are hereby incorporated by reference herein.

1. An image display apparatus, comprising: a plurality of pixels; asignal processing circuit; and a control circuit, wherein: each of theplurality of pixels comprises subsidiary pixels corresponding to four ormore primary colors; the plurality of pixels are arranged such thatsubsidiary pixels corresponding to a same color are arranged in a firstdirection; the signal processing circuit performs a signal processing tooutput a signal for designating intensity of each subsidiary pixelsconstituting a pixel, based on an input signal for designating a colorto be displayed in the pixel; the control circuit selects a conditionfor the signal processing to output a signal for designating intensityof each of subsidiary pixels constituting a first pixel, such thatsubsidiary pixels constituting the first pixel except for a subsidiarypixel which corresponds to a specific color is used; and the controlcircuit further selects a condition for the signal processing to outputa signal for designating intensity of each subsidiary pixelsconstituting a second pixel adjacent to the first pixel in the firstdirection, such that, among the subsidiary pixels constituting thesecond pixel, a subsidiary pixel which corresponds to a specific coloris used.
 2. An image display apparatus, comprising: a plurality ofpixels; a signal processing circuit; and a control circuit, wherein:each of the plurality of pixels has subsidiary pixels corresponding tofour or more primary colors; the signal processing circuit performssignal processing to output a signal for designating intensity of eachsubsidiary pixels constituting a pixel, based on an input signal fordesignating a color to be displayed in the pixel; the control circuitselects a condition, for a first image, for the signal processing tooutput a signal for designating intensity of each of subsidiary pixelsconstituting a first pixel, such that the subsidiary pixels constitutingthe first pixel except for a subsidiary pixel which corresponds to aspecific color is used; and the control circuit further selects acondition, for a second image adjacent in time to the first image, forthe signal processing to output a signal for designating intensity ofeach subsidiary pixels constituting the first pixel, such that, amongthe subsidiary pixels constituting the first pixel, a subsidiary pixelwhich corresponds to a specific color is used.
 3. An image displayapparatus according to claim 1, wherein: the signal processing circuitcomprises: a first circuit for performing signal processing under thecondition that the subsidiary pixel except for one corresponding to aspecific color is used; and a second circuit for performing signalprocessing under the condition that the subsidiary pixel correspondingto a specific color is used; and the control circuit selectivelydesignates one of the first circuit and the second circuit included inthe signal processing circuit.
 4. An image display apparatus accordingto claim 2, wherein: the signal processing circuit comprises: a firstcircuit for performing signal processing under the condition that thesubsidiary pixel except for one which corresponds to a specific color isused; and a second circuit for performing signal processing under thecondition that the subsidiary pixel which corresponds to a specificcolor is used; and the control circuit selectively designates one of thefirst circuit and the second circuit included in the signal processingcircuit.
 5. An image display apparatus according to claim 1, wherein acondition for the signal processing is selected based on pixel positioninformation.
 6. An image display apparatus according to claim 1, whereina condition for the signal processing is selected based on randomnumbers.
 7. An image display apparatus according to claim 1, wherein acondition for the signal processing is selected based on frameinformation for display.